OK wise guy Al, I guessed the mallard duck part, but I was confused by the "flank" part.
Is the flank of a bird the wing (I guess no), or the feathers from the side of the body, like a flake steak (I guess yes), or something else completely?

Sorry, didn't mean to be a wise guy, Greg. Flank feathers are from the side as the name implies. (I'm not sure if wing feathers are used in tying?) Flank feathers are in counter distinction to breast or neck feathers and are prized for their water resistence in dry fly and classic salmon patterns.

I found this gem:<!--http--><a href="http://www.flyanglersonline.com/flytying/tyingterms/" target="_blank"> fly tying terms</a><!--url-->

Under F for flank we find,
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"<b>Flank Feather:</b> Feathers found on the sides, either over, under or behind the base of the wings of birds"
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